The invention relates to an optoelectronic image sensor for a color camera where the proximity-focussed image intensifier is coupled to a two-dimensional semiconductor sensor.
In order to increase the light-sensitivity of a color camera by means of a semiconductor sensor, it is known to interpose a proximity-focussed image intensifier upstream of the semiconductor sensor with the color coding filter disposed directly in front of the flat photocathode of the proximity-focussed image intensifier (German Patent No. 36 18 646 A1). In case of a two-dimensional semiconductor sensor, the color coding filter is a mosaic filter. As compared to other known arrangements (German Patent No. 36 18 647 A1), this arrangement advantageously makes use of only one semiconductor sensor.
Due to the small dimensions of the light-sensitive surfaces of the semiconductor, each of which is associated with one pixel, and due to the correspondingly small individual surfaces of the mosaic filter, an exact registration of this mosaic filter with the semiconductor sensor is extremely difficult. An exact registration is required, however, to obtain a correct color reproduction.
Further, the British Patent No. 2,107,150 discloses an optoelectronic image sensor where the color stripe filter is mounted to the outside of a fiber glass input window of a microchannel image intensifier. In this known image sensor, the light, which is hence filtered according to separate colors, is first fed through the fiber optic pane to the photocathode. The problem here is that, on the one side, the individual glass fibers do not have the desired small thickness and, on the other hand, they are not exactly parallel to one another. This unparallelism of the glass fibers can cause distortions of 50 to 100 .mu.m. The geometrical reproduction of the color stripes on the photocathode is hence not sufficiently accurate. In addition, there are errors caused by the microchannel image intensifier itself due to the large range of the electrons emanating from the microchannel plate and errors caused by the optical transmission of the image from the viewing screen to the semiconductor sensor. These latter errors are caused by flaws in the fiber optic pane between the viewing screen and the semiconductor similar to the already described errors between the color stripe filter and the photocathode, and, further, caused by the lack of fiber-fiber coincidence when two fiber optic panes are coupled.
The described image reproduction errors cause the light, which is intensified and filtered by a color stripe, to arrive not only at the corresponding column of the semiconductor sensor but also at adjacent columns. The purposes of the latter, however, is the optoelectronic sensing of other color components. The result is a false color response.